1. Technical Field
The present invention relates to a new phase shift full bridge (PSFB) converter using a clamp circuit connected to the center tap of transformer on the secondary side and an operating method thereof.
2. Description of the Related Art
A pulse with modulation (PWM) phase shift full bridge (PSFB) is widely applied in the power range of several kW for a battery charger. The PWM PSFB has advantages in that primary switches can achieve a zero-voltage switching turn-on operation and can be simply controlled compared to a frequency-modulation converter. However, when the PWM PSFB is applied to a battery charger for electric vehicles, the following disadvantages may be present. First, a conduction loss increases due to a high circulation current because the range of an output voltage is very wide. Voltage stress in a rectification stage seriously increases and a switching loss occurring in the rectification stage is very large because an output voltage is large and a large reverse recovery current flows on the secondary side. Next, there is a problem in that the size of the output filter stage is increased because the output voltage is large.
Lots of researches have been carried out to improve the disadvantages of the PSFB. First, a full bridge converter in which the frequency shifts was proposed in order to obviate a circulation current and to reduce the size of an output inductor. However, there is a problem in that the optimal design of a magnetic substance or an electric condenser becomes difficult because an operating frequency is very widely changed with respect to an output voltage range. Many active clamp schemes have been introduced to reduce the voltage stress of a rectification stage on the secondary side. However, there are problems in that power density is lowered and the reliability of the circuit is degraded because switches are additionally used. Research for reducing the switching loss of the rectification stage on the secondary side has been carried out, but there is a problem in that an additional conduction loss and a switching loss occur because the switch is positioned in the path along which power is transferred.